Methods and system for separating carbon dioxide from syngas

ABSTRACT

A system for use in separating carbon dioxide and acid gas from syngas includes a syngas purification circuit that includes at least one adsorption tower coupled in flow communication to a supply of lean solvent. The system further includes a carbon dioxide removal circuit coupled downstream from the syngas purification circuit. The carbon dioxide removal circuit includes at least one component that facilitates the removal of carbon dioxide from the solvent after the solvent has passed through the syngas purification circuit. The carbon dioxide removal circuit also includes at least one compressor, wherein the at least one component and the at least one compressor are operable at substantially similar pressures. In addition, the system includes an acid gas removal circuit that is coupled downstream from the carbon dioxide removal circuit. The acid gas removal circuit includes at least one adsorption tower.

BACKGROUND OF THE INVENTION

The field of the invention relates generally to the removal of acid gas from syngas, and more particularly to methods and systems for use in separating high pressure carbon dioxide from syngas for use in a gasifier or other systems.

At least some known acid gas removal systems in integrated gasification combined cycle (IGCC) systems are designed to remove sulfur, and more particularly hydrogen sulfide, from the syngas to very low levels. Furthermore, at least some known IGCC systems pass carbon dioxide into the syngas at a rate such that the mass flow to the combustion turbine is high and the hydrogen sulfide concentration in the acid gas to the solvent recovery unit (SRU) is high.

Unrefrigerated chemical and physical solvents, such as amines and DEPG (“dimethyl ethers of polyethylene glycols”), have been used in at least some known IGCC acid gas removal systems due to the higher power consumption required to achieve and maintain refrigeration. Furthermore, although both refrigerated and unrefrigerated chemical and physical solvents have been used in IGCC systems with carbon dioxide removal and/or recovery, such systems are designed to remove pure carbon dioxide with very low levels of hydrogen sulfide. However, carbon dioxide including an amount of hydrogen sulfide separated at higher pressures may be useful as a feed stream to at least some known gasification systems.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, a system for use in separating carbon dioxide and acid gas from syngas is provided. The system includes a syngas purification circuit that includes at least one adsorption tower coupled in flow communication to a supply of lean solvent. The system further includes a carbon dioxide removal circuit coupled downstream from the syngas purification circuit. The carbon dioxide removal circuit includes at least one component that facilitates the removal of carbon dioxide from the solvent after the solvent has passed through the syngas purification circuit. The carbon dioxide removal circuit also includes at least one compressor, wherein the at least one component and the at least one compressor are operable at substantially similar pressures. In addition, the system includes an acid gas removal circuit that is coupled downstream from the carbon dioxide removal circuit. The acid gas removal circuit includes at least one adsorption tower.

In another aspect, a system for use in separating carbon dioxide and acid gas from syngas is provided. The system includes at least one acid gas absorption tower coupled in flow communication with a supply of lean solvent, wherein the at least one acid gas absorption tower is configured to produce a purified stream of syngas. The system further includes a solvent circuit coupled in flow communication with at least one acid gas adsorption tower. The solvent circuit comprises at least one component that facilitates removing carbon dioxide from the solvent, wherein the at least one component is operable at a first pressure. In addition, the system includes a compressor circuit coupled in flow communication with the solvent circuit. The compressor circuit comprises at least one compressor that is operable at a second pressure, wherein the first pressure and second pressure are substantially similar. The system also includes an acid gas removal solvent stripper coupled in flow communication with the solvent circuit and the at least one acid gas adsorption tower.

In a further aspect, a method of assembling a syngas purification system is provided. The method includes providing at least one acid gas absorption tower, coupling a lean solvent supply line to the at least one acid gas absorption tower, and coupling a syngas supply line to the at least one acid gas absorption tower, wherein the at least one acid gas absorption tower is configured to produce a purified stream of syngas. The method further includes coupling at least one flash unit downstream from the acid gas absorption tower, wherein the at least one flash unit is operable at a first pressure and is configured to produce a stream of carbon dioxide. The method also includes coupling at least one compressor unit downstream from the at least one flash unit, wherein the at least one compressor unit is operable at a second pressure that is substantially similar to the first pressure, and coupling an acid gas removal solvent stripper downstream from the at least one flash unit, wherein the acid gas removal solvent stripper is configured to produce a stream of acid gas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a first embodiment of a system for use in separating carbon dioxide from syngas;

FIG. 2 is a schematic view of a second embodiment of a system for use in separating carbon dioxide from syngas; and

FIG. 3 is a schematic view of a third embodiment of a system for use in separating carbon dioxide from syngas.

DETAILED DESCRIPTION OF THE INVENTION

It is desirable to provide a system for separating carbon dioxide from syngas produced in an IGCC through the use of a solvent that is both cost efficient and operationally efficient. A solvent may be categorized as lean, semi-rich, or rich depending on the amount of acid gas and/or carbon dioxide present in the solvent. A solvent containing high amounts of acid gas and/or carbon dioxide is considered a rich solvent. A solvent containing low amounts of acid gas and/or carbon dioxide is considered a lean solvent. More particularly, a rich solvent is a solvent that has absorbed acid gas (e.g., H₂S and CO₂) from the raw syngas or acid gas containing process gas. A semi-rich solvent is solvent that has absorbed mostly CO₂ and some H₂S from syngas or acid gas containing process gas. Additionally, a lean solvent is either rich or semi-rich solvent that has been stripped or regenerated to remove most of the acid gas.

FIG. 1 is a schematic diagram of a system 100 that may be used to separate carbon dioxide from syngas. In the exemplary embodiment, system 100 includes a syngas purification circuit 102, a carbon dioxide removal circuit 104, and an acid gas removal circuit (AGR circuit) 106. More specifically, syngas purification circuit 102 includes an acid gas absorption tower 108, and acid gas removal circuit 106 includes an Acid Gas Removal (AGR) solvent stripper 110. Moreover, carbon dioxide removal circuit 104 includes a compressor circuit 112, a semi-rich solvent circuit 114, and a rich solvent circuit 116. In the exemplary embodiment, syngas purification circuit 102 is coupled in flow communication with AGR circuit 106 via rich solvent circuit 116. Syngas purification circuit 102 is also coupled in flow communication with semi-rich solvent circuit 114. Moreover, compressor circuit 112 is coupled in flow communication with semi-rich solvent circuit 114, rich solvent circuit 116, and a gasification system (not shown). Compressor circuit 112 supplies high-pressure carbon dioxide (CO2) to a gasification system (not shown).

Acid gas absorption tower 108 includes a plurality of vertically stacked trays 118 therein. A lean solvent supply line 120 is coupled in flow communication with tower 108. In the exemplary embodiment, lean solvent supply line 120 includes a lean solvent cooler 122 through which a lean solvent (not shown) passes before entering tower 108. Further, tower 108 includes a syngas outlet 124 that channels clean syngas (not shown) from system 100. A syngas supply line 126 is coupled in flow communication with tower 108 at a bottom tray 128. Furthermore, in the exemplary embodiment, tower 108 includes an absorber reboiler 130 that is coupled to rich solvent circuit 116 via an inlet 132. More specifically, a rich solvent (not shown) is discharged from tower 108, at bottom tray 128, into rich solvent circuit 116 through absorber reboiler 130 and inlet 132. At a first intermediate point 134, tower 108 is coupled to semi-rich solvent circuit 114 via an inlet 135. At a second intermediate point 136 several trays 118 downstream and generally vertically upward from first intermediate point 134, tower 108 includes an outlet 137 coupled to semi-rich solvent circuit 114.

In the exemplary embodiment, compressor circuit 112 includes first, second, and third carbon dioxide compressors 138, 140, and 142, respectively, and semi-rich solvent circuit 114 includes a first, second, and third flash unit 144, 146, and 148, respectively. First flash unit 144 is coupled upstream from, and in flow communication with, first compressor 138 via outlet portion 150 and second flash unit 146 via outlet portion 152. Second flash unit 146 is further coupled upstream from, and in flow communication with, second compressor 140 via outlet portion 154 and third flash unit 148 via outlet portion 156. Third flash unit 148 is coupled upstream from, and in flow communication with, third compressor 142 via outlet portion 158. Semi-rich solvent circuit 114 also includes a semi-rich solvent return pump 160 that returns semi-rich solvent (not shown) to tower 108. Return pump 160 is coupled downstream from an exit portion 162 of third flash unit 148. Furthermore, in the exemplary embodiment, third compressor unit 142 is coupled upstream from, and in flow communication with, second compressor unit 140, and second compressor unit 140 is coupled upstream from, and in flow communication with, first compressor 138.

Rich solvent circuit 116, in the exemplary embodiment, includes first and second flash units 163 and 164, respectively. First flash unit 163 is coupled upstream from, and in flow communication with, first compressor 138 via outlet portion 166 and second flash unit 164 via outlet portion 168. Second flash unit 164 is coupled upstream from, and in flow communication with, second compressor unit 140 via outlet portion 170. Rich solvent circuit 116 also includes a heat exchanger 172. Heat exchanger 172 is coupled between an outlet portion 174 of second flash unit 164 and AGR solvent stripper 110. Heat exchanger 172 also includes an outlet portion 176 for directing lean solvent (not shown) to acid gas absorption tower 108. Additionally, in the exemplary embodiment, rich solvent circuit 116 includes a pump 178 coupled between AGR solvent stripper 110 and heat exchanger 172.

In the exemplary embodiment, AGR solvent stripper 110 includes a plurality of vertically-stacked trays 180 therein. At an intermediate point 182 of AGR solvent stripper 110, a supply line 184 from rich solvent circuit 116 is coupled in flow communication with AGR solvent stripper 110. Furthermore, in the exemplary embodiment, AGR solvent stripper 110 includes an external reflux system 186 that includes an outlet portion 188 of system 100. More specifically, external reflux system 186 includes a condenser 190 and a reflux drum 192 coupled in flow communication to AGR solvent stripper 110 such that at least a portion of a light boiling point fraction is condensed for reflux to AGR solvent stripper 110. AGR solvent stripper 110 also includes a solvent stripper reboiler 194 that includes an inlet 196 to rich solvent circuit 116. More specifically, a rich solvent (not shown) is discharged from AGR solvent stripper 110 at a stripper bottom 198 into rich solvent circuit 116 through stripper solvent reboiler 194 and inlet 196.

In operation, syngas containing carbon dioxide is supplied to acid gas absorption tower 108 at bottom tray 128. As is described in more detail below, recycle solvent is supplied to acid gas absorption tower 108 at second intermediate point 136 via semi-rich solvent return pump 160. In the exemplary embodiment, lean solvent (not shown) is supplied to the top of acid gas absorption tower 108 via lean solvent cooler 122 to facilitate stripping hydrogen sulfide from syngas.

Solvent containing carbon dioxide is discharged from acid gas absorption tower 108 at first intermediate point 134 and is channeled to first flash unit 144 of semi-rich solvent circuit 114 wherein carbon dioxide is separated from the solvent. Carbon dioxide exits first flash unit 144 via outlet portion 150 and is channeled to first compressor 138. In the exemplary embodiment, first flash unit 144 and first compressor unit 138 are operable at substantially similar pressures. Solvent containing some carbon dioxide exits first flash unit 144 via outlet portion 152 and is channeled to second flash unit 146 wherein carbon dioxide is further separated from the solvent. Carbon dioxide exits second flash unit 146 via outlet portion 154 and is channeled to second compressor 140. In the exemplary embodiment, second flash unit 146 and second compressor 140 are operable at substantially similar pressures. Solvent containing any remaining carbon dioxide exits second flash unit 146 via outlet portion 156 and is channeled to third flash unit 148 wherein remaining carbon dioxide is further separated from the solvent. Carbon dioxide exits third flash unit 148 via exit portion 158 and is channeled to third compressor 142. In the exemplary embodiment, third flash unit 148 and third compressor 142 are operable at substantially similar pressures.

In the exemplary embodiment, carbon dioxide exiting third compressor 142 is channeled to second compressor 140, and carbon dioxide exiting second compressor is channeled to first compressor 138 wherein it is further compressed, and recycled for gasification or other purposes. Solvent exits third flash unit 148 via outlet portion 162, is channeled through semi-rich solvent recovery pump 160, and enters acid gas absorption tower 108 at second intermediate point 136. Clean syngas is discharged from acid gas absorption tower 108 and is collected for further use.

Rich solvent exits acid gas absorption tower 108 and is channeled to first flash unit 163 wherein carbon dioxide is separated from the solvent. Carbon dioxide exits first flash unit 163 via outlet portion 166 and is channeled to first compressor 138. Solvent containing carbon dioxide exits first flash unit 163 via outlet portion 168 and is channeled to second flash unit 164 wherein remaining carbon dioxide is further separated from the solvent. Carbon dioxide exits second flash unit 164 via outlet portion 170 and is channeled to second compressor 140. Solvent containing any remaining carbon dioxide is discharged from second flash unit 164 via outlet portion 174 and is channeled to AGR solvent stripper 110 through heat exchanger 172.

AGR solvent stripper 110 facilitates reducing the level of hydrogen sulfide and COS (carbon oxides) in the solvent. A light boiling fraction is recovered through AGR solvent stripper 110. Lean solvent collected at AGR solvent stripper 110 is channeled to reboiler 194.

In the exemplary embodiment, solvent exits AGR solvent stripper 110 and enters reboiler 194, which further facilitates removing carbon dioxide from the solvent exiting AGR solvent stripper 110. One portion of the solvent exits reboiler 194 and is returned into AGR solvent stripper 110. The remaining portion of the solvent exits reboiler 194 and is channeled through heat exchanger 172 to be recycled to acid gas absorption tower 108.

The solvent rates and the operating temperatures are dependent on the type of solvent used. In some embodiments, the solvents employed are organic solvents such as light hydrocarbons (naphtha range), methanol and mixtures of the DEPG.

FIG. 2 is a schematic diagram of a system 200 that may be used for separating carbon dioxide from syngas. In the exemplary embodiment, system 200 includes a syngas purification circuit 202, a carbon dioxide removal circuit 204, and an AGR solvent stripper circuit 206. More specifically, syngas purification circuit 202 includes a first acid gas absorption tower 208 and a second acid gas absorption tower 210, and acid gas removal circuit 206 includes an Acid Gas Removal (AGR) solvent stripper 212. Carbon dioxide removal circuit 204 includes a compressor circuit 214, a semi-rich solvent circuit 216, and a rich solvent circuit 218. In the exemplary embodiment, syngas purification circuit 202 is coupled in flow communication with AGR circuit 206 through rich solvent circuit 218. Syngas purification circuit 202 is also coupled in flow communication with semi-rich solvent circuit 216. Moreover, compressor circuit 214 is coupled in flow communication with semi-rich solvent circuit 216, rich solvent circuit 218, and a gasification system (not shown). Compressor circuit 214 supplies high-pressure carbon dioxide (CO₂) to a gasification system.

Syngas purification circuit 202 includes first and second acid gas absorption towers 208 and 210, respectively, that each include a plurality of vertically-stacked trays 220 therein. A lean solvent supply line 222 is coupled in flow communication with a top 224 of second tower 210. Lean solvent supply line 222 includes a lean solvent cooler 226 through which a lean solvent (not shown) passes before entering second tower 210. Furthermore, second tower 210 includes a syngas outlet 228 for use in channeling clean syngas from system 200. In the exemplary embodiment, at an intermediate point 230, second tower 210 includes outlet portion 232 of semi-rich solvent circuit 216.

In the exemplary embodiment, second tower 210 is coupled downstream from, and in flow communication with, first tower 208 via a syngas supply line 234 and a recycle solvent supply line 236. More specifically, syngas supply line 234 is coupled between an outlet portion 238 positioned at a top 239 of first tower 208 and an inlet portion 240 positioned at a bottom 241 of second tower 210. Recycle solvent supply line 236 is coupled between an inlet portion 242 positioned at the top 239 of first tower 208 and an outlet portion 244 positioned at the bottom 241 of second tower 210. In the exemplary embodiment, recycle solvent supply line 236 includes an outlet portion 246 that supplies a portion of recycle solvent to semi-rich solvent circuit 216 a pump 248 through which recycled solvent (not shown) passes before entering first tower 208. Furthermore, in the exemplary embodiment, first tower 208 also includes an absorber reboiler 250 that includes an inlet 252 to rich solvent circuit 218. More specifically, a rich solvent (not shown) is discharged from first tower 208 at a bottom tray 254 into rich solvent circuit 218 through absorber reboiler 250 and inlet 252.

In the exemplary embodiment, compressor circuit 214 includes first, second and third compressors 256, 258, and 260, respectively, and semi-rich solvent circuit 216 includes first, second, and third flash units 258, 264, and 266, respectively. First flash unit 258 is coupled upstream from, and in flow communication with, first compressor 256 via an outlet portion 268 and second flash unit 264 via outlet portion 270. Second flash unit 264 is also coupled upstream from, and in flow communication with, second compressor 258 via outlet portion 272 and third flash unit 266 via outlet portion 274. Third flash unit 266 is coupled upstream from, and in flow communication with, third compressor 260 via outlet portion 276. Semi-rich solvent circuit 216 also includes a semi-rich solvent return pump 278 that returns semi-rich solvent to second tower 210. Return pump 278 is coupled downstream from exit portion 280. Furthermore, in the exemplary embodiment, third compressor unit 260 is coupled upstream from, and in flow communication with, second compressor unit 258, and second compressor unit 258 is coupled upstream from, and in flow communication with, first compressor 256.

Rich solvent circuit 218, in the exemplary embodiment, includes first and second flash units 282 and 284, respectively. First flash unit 282 is coupled upstream from, and in flow communication with, first compressor 256 via outlet portion 286 and second flash unit 284 via outlet portion 288. Second flash unit 284 is coupled upstream from, and in flow communication with, second compressor unit 258 via outlet portion 290. Rich solvent circuit 218 also includes a heat exchanger 292. Heat exchanger 292 is coupled between outlet portion 294 of second flash unit 284 and AGR solvent stripper 212. Heat exchanger 292 includes an outlet portion 296 that directs lean solvent to second tower 210. Additionally, in the exemplary embodiment, rich solvent circuit 218 includes a pump 298 that is coupled between AGR solvent stripper 212 and heat exchanger 292.

In the exemplary embodiment, AGR solvent stripper 212 includes a plurality of vertically-stacked trays 300 therein. A supply line 302 from rich solvent circuit 218 is coupled in flow communication with AGR solvent stripper 212 at an intermediate point 304. AGR solvent stripper 212 also includes an external reflux system 306 that includes an outlet portion 308 of system 200. More specifically, external reflux system 306 includes a condenser 310 and a reflux drum 312 that are coupled in flow communication to AGR solvent stripper 212 such that at least a portion of a light boiling point fraction is condensed for reflux to the top of AGR solvent stripper 212. Furthermore, in the exemplary embodiment, AGR solvent stripper 212 includes a solvent stripper reboiler 314 that includes an inlet 316 to rich solvent circuit 218.

In operation, syngas containing carbon dioxide (not shown) is supplied to a bottom one of the vertically-stacked trays 220 of first tower 208. As is described in more detail below, recycle solvent exits second tower 210 and enters first tower 208 via recycle solvent supply line 236. More specifically, in the exemplary embodiment, recycle solvent exits second tower 210 at outlet portion 244, passes through pump 248, and enters first tower 208 at inlet portion 242. Furthermore, in the exemplary embodiment, a rich solvent (not shown) is discharged from first tower 208 and is channeled through reboiler 250. A portion of the rich solvent exiting reboiler 250 enters first tower 208 and the remaining portion enters rich solvent circuit 218. Moreover, in the exemplary embodiment, a first cleaned portion of syngas exits first tower 208 at outlet portion 238 and enters second tower 210 at inlet portion 240.

In the exemplary embodiment, lean solvent (not shown) is supplied to the top 224 of second tower 210 via lean solvent cooler 226 to facilitate stripping hydrogen sulfide from syngas.

As described above, recycle solvent containing carbon dioxide exits second tower 210 at outlet portion 244. A portion of recycle solvent is channeled to first tower 208 via pump 248 and recycle solvent supply line 236, and the remaining portion is channeled to first flash unit 262 wherein carbon dioxide is separated from the solvent. Carbon dioxide exits first flash unit 262 via outlet portion 268 and is channeled to first compressor 256. In the exemplary embodiment, first flash unit 262 and first compressor 256 are operable at substantially similar pressures. Solvent containing carbon dioxide exits first flash unit 262 via outlet portion 270 and is channeled to second flash unit 264 wherein carbon dioxide is further separated from the solvent. Carbon dioxide exits second flash unit 264 via outlet portion 272 and is channeled to second compressor 258. In the exemplary embodiment, second flash unit 264 and second compressor 258 are operable at substantially similar pressures. Solvent containing carbon dioxide exits second flash unit 264 via outlet portion 274 and is channeled to third flash unit 266 wherein any remaining carbon dioxide is further separated from the solvent. Carbon dioxide exits third flash unit 266 via exit portion 276 and is channeled to third compressor 260. In the exemplary embodiment, third flash unit 266 and third compressor 260 are operable at substantially similar pressures.

In the exemplary embodiment, carbon dioxide exiting third compressor 260 is channeled to second compressor 258, and carbon dioxide exiting second compressor 258 is channeled to first compressor 256 wherein it is further compressed, and recycled for gasification or other purposes. Solvent exits third flash unit 266 via outlet portion 280, is channeled through semi-rich solvent recovery pump 278, and enters second tower 210 at intermediate point 230. Clean syngas is discharged from second tower 210 and is collected for further use.

Rich solvent exits first tower 208 and is channeled to first flash unit 282 wherein carbon dioxide is separated from the solvent. Carbon dioxide exits first flash unit 282 via outlet portion 282 and is channeled to first compressor 256. Solvent containing some carbon dioxide exits first flash unit 282 via outlet portion 288 and is channeled to second flash unit 284 wherein remaining carbon dioxide is further separated from the solvent. Carbon dioxide exits second flash unit 284 via outlet portion 290 and is channeled to second compressor 258. Solvent containing any remaining carbon dioxide exits second flash unit 284 via outlet portion 294 and is channeled to AGR solvent stripper through heat exchanger 292.

AGR solvent stripper 212 facilitates reducing the level of hydrogen sulfide and carbon oxides in the solvent. A light boiling fraction is recovered through AGR solvent stripper 212. Lean solvent collected at the bottom of AGR solvent stripper 212 is channeled to reboiler 314.

In the exemplary embodiment, solvent exits AGR solvent stripper 212 and enters reboiler 314, which further facilitates removal of carbon dioxide from the solvent exiting AGR solvent stripper 212. One portion of the solvent exits reboiler 314 and is channeled back into AGR solvent stripper 212. The remaining portion of the solvent exits reboiler 314 and is channeled through heat exchanger 292 to be recycled to second tower 210.

The solvent rates and the operating temperatures will depend on the solvent used. In some embodiments, the solvents employed are organic solvents such as light hydrocarbons (naphtha range), methanol and mixtures of the DEPG.

FIG. 3 is a schematic diagram of a system 400 that may be used for separating carbon dioxide from syngas. More specifically, system 400 includes a syngas purification circuit 402, a carbon dioxide removal circuit 404, and an acid gas removal circuit (AGR circuit) 406. More specifically, syngas purification circuit 402 includes an acid gas absorption tower 408, and acid gas removal circuit 406 includes an Acid Gas Removal (AGR) solvent stripper 410. Carbon dioxide removal circuit 404 includes a compressor circuit 412 and a rich solvent circuit 414. In the exemplary embodiment, syngas purification circuit 402 is coupled in flow communication with AGR circuit 406 through rich solvent circuit 414. Moreover, compressor circuit 412 is coupled in flow communication with rich solvent circuit 414 and a gasification system (not shown). Compressor circuit 412 supplies high-pressure carbon dioxide (CO2) to a gasification system.

Acid gas absorption tower 408 includes a plurality of vertically-stacked trays 416 therein. A lean solvent supply line 418 is coupled in flow communication with the top of tower 408. Lean solvent supply line 418 includes a lean solvent cooler 420 through which a lean solvent (not shown) passes before entering tower 408. Further, tower 408 includes a syngas outlet 422 for discharging clean syngas (not shown) from system 400. A syngas supply line 424 is coupled in flow communication with tower 408 at a bottom tray 426.

In the exemplary embodiment, compressor circuit 412 includes a first carbon dioxide compressor 434, and rich solvent circuit 414 includes a first flash unit 436. First flash unit 436 is coupled upstream from, and in flow communication with, first compressor 434 via outlet portion 438. Further, first flash unit 436 is coupled upstream from, and in flow communication with, AGR solvent stripper 410 via outlet portion 440. In an alternative embodiment, compressor circuit 412 includes any number of compressors, and rich solvent circuit may include any number of flash units.

Rich solvent circuit 414, in the exemplary embodiment, includes a lean solvent return pump 442 and a heat exchanger 444. Lean solvent return pump 442 is coupled downstream from AGR solvent stripper 410 and is upstream from heat exchanger 444. Heat exchanger 442, in the exemplary embodiment, is also coupled between an outlet portion 446 of syngas purification circuit 402 and first flash unit 436. Heat exchanger 444 also includes an outlet portion 448 for directing lean solvent (not shown) to acid gas absorption tower 408.

In the exemplary embodiment, AGR solvent stripper 410 includes a plurality of vertically-stacked trays 450 therein. At an intermediate point 452 of AGR solvent stripper 410, a supply line 454 from rich solvent circuit 414 is coupled in flow communication with AGR solvent stripper 410. Furthermore, in the exemplary embodiment, AGR solvent stripper 410 includes an external reflux system 456, which includes an outlet portion 458 of system 400. More specifically, external reflux system 456 includes a condenser 460 and a reflux drum 462 coupled in flow communication to AGR solvent stripper 410 such that at least a portion of a light boiling point fraction is condensed for reflux to AGR solvent stripper 410. AGR solvent stripper 410 also includes a solvent stripper reboiler 464 that includes an inlet 466 to rich solvent circuit 414. More specifically, a rich solvent (not shown) is discharged from AGR solvent stripper 410 at a stripper bottom 468 into rich solvent circuit 414 through stripper solvent reboiler 464 and inlet 466.

In operation, syngas (not shown) containing carbon dioxide is channeled to acid gas absorption tower 408 at bottom tray 426. In the exemplary embodiment, lean solvent (not shown) is supplied to the top of acid gas absorption tower 408 via lean solvent cooler 420 to facilitate stripping hydrogen sulfide from syngas.

Solvent containing carbon dioxide exits acid gas absorption tower 408 at bottom tray 426 and is channeled to heat exchanger 448 and then to first flash unit 436 of rich solvent circuit 414 wherein carbon dioxide is separated from the solvent. Carbon dioxide exits first flash unit 436 via outlet portion 438 and is channeled to first compressor 434. In the exemplary embodiment, first flash unit 436 and first compressor unit 434 are operable at substantially similar pressures. Solvent containing some carbon dioxide exits first flash unit 436 via outlet portion 440 and is channeled to AGR solvent stripper 410.

AGR solvent stripper 410 facilitates reducing the level of hydrogen sulfide and COS (carbon oxides) in the solvent. A light boiling fraction is recovered through the top of AGR solvent stripper 410. Lean solvent collected at the bottom of AGR solvent stripper 410 is channeled to reboiler 464.

In the exemplary embodiment, solvent exits AGR solvent stripper 410 and enters reboiler 464, which further facilitates removal of carbon dioxide from the solvent exiting AGR solvent stripper 410. One portion of the solvent exits reboiler 464 and is channeled back into AGR solvent stripper 410. The remaining portion of the solvent exits reboiler 464 and is channeled through pump 442, heat exchanger 444, and cooler 420 to be recycled to acid gas absorption tower 408.

The solvent rates and the operating temperatures will depend on the solvent used. In some embodiments, the solvents employed are organic solvents such as light hydrocarbons (naphtha range), methanol and mixtures of the DEPG.

The methods and systems described herein enable a stream of syngas to be separated into a purified syngas stream, a compressed carbon dioxide stream, and an acid gas stream. Separating carbon dioxide from syngas, wherein the carbon dioxide contains amounts of hydrogen sulfide, facilitates improving an IGCC system efficiency because a lower level of energy is required to separate sour carbon dioxide from syngas than is required to separate pure carbon dioxide from syngas. The use of the solvent in the process facilitates reducing a solvent circulation rate which facilitates reducing the utilities and refrigeration load required for the process. Furthermore, the use of a lightly cooled solvent facilitates reducing the heat required for use in the AGR solvent stripper reboiler to lower than that of low pressure steam. The ability to use a lower level of heat facilitates improving the efficiency of the IGCC system. The description above is meant to cover a specific example of the general process for separating carbon dioxide and acid gas from syngas and should not be found limited to the specific embodiment described.

Exemplary embodiments of methods and systems for purifying a stream of syngas are described above in detail. The methods and systems are not limited to the specific embodiments described herein nor to the specific illustrated systems, but rather, steps of the method and/or components of the systems may be utilized independently and separately from other steps and/or components described herein. Further, the described method steps and/or system components can also be defined in, or used in combination with, other methods and/or systems, and are not limited to practice with only the method and system described herein. The description above is meant to cover a specific example of the general process for separating carbon dioxide and acid gas from syngas and should not be found limited to the specific embodiment described.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

1. A system for use in separating carbon dioxide and acid gas from syngas comprising: a syngas purification circuit comprising at least one adsorption tower coupled in flow communication to a supply of lean solvent; a carbon dioxide removal circuit coupled downstream from said syngas purification circuit, said carbon dioxide removal circuit comprising at least one component that facilitates the removal of carbon dioxide from the solvent after the solvent has passed through said syngas purification circuit and at least one compressor, wherein the at least one component and the at least one compressor are operable at substantially similar pressures; and an acid gas removal circuit coupled downstream from said carbon dioxide removal circuit, said acid gas removal circuit comprising at least one adsorption tower.
 2. A system in accordance with claim 1, wherein said carbon dioxide removal circuit further comprises a compressor circuit, a rich solvent circuit, and a semi-rich solvent circuit.
 3. A system in accordance with claim 2, wherein said compressor circuit comprises a first compressor unit, a second compressor unit, and a third compressor unit coupled together in a serial flow arrangement.
 4. A system in accordance with claim 3, wherein said semi-rich solvent circuit comprises a first flash unit, a second flash unit, and a third flash unit coupled together in a serial flow arrangement.
 5. A system in accordance with claim 4, wherein said first compressor unit and said first flash unit are operable at substantially similar pressures, said second compressor unit and said second flash unit are operable at substantially similar pressures, and said third compressor unit and said third flash unit are operable at substantially similar pressures.
 6. A system in accordance with claim 5, wherein said semi-rich solvent circuit further comprises a heat exchanger configured to: increase a temperature of solvent exiting said semi-rich solvent circuit; and to decrease a temperature of solvent channeled from said solvent stripper circuit to said syngas purification circuit.
 7. A system in accordance with claim 3, wherein said rich solvent circuit comprises a first flash unit and a second flash unit, wherein said first flash unit and said first compressor unit are operable at substantially similar pressures, and wherein said second flash unit and said second compressor unit are operable at substantially similar pressures.
 8. A system in accordance with claim 2, wherein said syngas purification circuit comprises an acid gas absorption tower configured to remove acid gas and carbon dioxide from syngas.
 9. A system in accordance with claim 8, wherein said semi-rich solvent circuit comprises a return pump that facilitates supplying lean solvent from said acid gas removal circuit to said acid gas absorption tower.
 10. A system in accordance with claim 9, wherein said syngas purification system further comprises a solvent cooler coupled upstream from said acid gas absorption tower, said solvent cooler is configured to reduce a temperature of solvent supplied to said acid gas absorption tower.
 11. A system in accordance with claim 10, wherein said solvent cooler facilitates reducing the solvent to a temperature of from about 0° C. to about 100° C.
 12. A system in accordance with claim 2, wherein said syngas purification circuit at least one adsorption column comprises a first acid gas absorption tower and a second acid gas absorption tower, said first and second acid gas absorption towers are configured to remove acid gas and carbon dioxide from syngas.
 13. A system in accordance with claim 12, wherein said semi-rich solvent circuit comprises a return pump that supplies lean solvent from said acid gas removal circuit to said second acid gas absorption tower.
 14. A system in accordance with claim 13, wherein said syngas purification system further comprises a solvent cooler coupled upstream from said second acid gas absorption tower, said solvent cooler configured to reduce a temperature of solvent supplied to said second acid gas absorption tower.
 15. A system in accordance with claim 14, wherein said solvent cooler facilitates reducing the solvent to a temperature of from about 0° C. to about 100° C.
 16. A system in accordance with claim 15, wherein said syngas purification circuit further comprises a solvent return pump configured to channel the solvent from said second acid gas absorption tower to said first acid gas absorption tower.
 17. A system for use in separating carbon dioxide and acid gas from syngas comprising: at least one acid gas absorption tower coupled in flow communication with a supply of lean solvent, said at least one acid gas absorption tower configured to produce a purified stream of syngas; a solvent circuit coupled downstream from and in flow communication with said at least one acid gas absorption tower, said solvent circuit comprises at least one component that facilitates removing carbon dioxide from the solvent, wherein said at least one component is operable at a first pressure; a compressor circuit coupled in flow communication with said solvent circuit, said compressor circuit comprises at least one compressor that is operable at a second pressure, wherein the first pressure and second pressure are substantially similar; and an acid gas removal solvent stripper coupled in flow communication with said solvent circuit and said at least one acid gas absorption tower.
 18. A system in accordance with claim 17 further comprising a lean solvent cooler coupled upstream from said at least one acid gas absorption tower, said cooler facilitates reducing a temperature of the supply of lean solvent entering said at least one acid gas absorption tower.
 19. A method of assembling a syngas purification system comprising: providing at least one acid gas absorption tower; coupling a lean solvent supply line to the at least one acid gas absorption tower; coupling a syngas supply line to the at least one acid gas absorption tower, wherein the at least one acid gas absorption tower is configured to produce a purified stream of syngas; coupling at least one flash unit downstream from said acid gas absorption tower, wherein the at least one flash unit is operable at a first pressure to produce a stream of carbon dioxide; coupling at least one compressor unit downstream from the at least one flash unit, wherein the at least one compressor unit is operable at a second temperature that is substantially similar to the first pressure; and coupling an acid gas removal solvent stripper downstream from the at least one flash unit, wherein the acid gas removal solvent stripper is configured to produce a stream of acid gas.
 20. A method in accordance with claim 19 further comprising coupling a second acid gas absorption tower in flow communication with the first acid gas absorption tower, wherein the second acid gas absorption tower facilitates removing of carbon dioxide and acid gas from a supply of syngas channeled through the syngas supply line. 